Platinum and tin-containing catalyst and use thereof in alkane dehydrogenation

ABSTRACT

In a process for preparing a dehydrogenation catalyst of the type in which a support comprising zinc aluminate is impregnated with at least one of platinum and tin from an impregnation solution, the improvement comprises simultaneously impregnating the support with the platinum and the tin by contacting the support with an impregnation solution which comprises, in solution, a tin compound, a platinum compound, and a carboxylic acid. The thus prepared catalyst can be employed in the dehydrogenation of at least one alkane containing 2-8 carbon atoms per molecule in the presence of steam.

BACKGROUND OF THE INVENTION

According to one aspect, this invention relates to a catalyst comprisingplatinum and tin on a zinc aluminate-containing support, and accordingto other aspects relates to a novel process for making such catalyst anduse of the catalyst in alkane dehydrogenation.

In the preparation of dehydrogenation catalysts comprising platinum andtin on a zinc aluminate-containing support, it is known to impregnatethe support with platinum and/or tin by contacting such support with animpregnation solution having at least one of a platinum compound or tincompound dissolved therein. However, improvement in such dehydrogenationcatalysts with respect to activity (i.e. conversion), selectivity toolefins, and rate of deactivation would be desirable.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide adehydrogenation catalyst comprising a zinc aluminate-containing supportwhich is impregnated with platinum and/or tin from an impregnationsolution, and which demonstrates improved performance in thedehydrogenation of alkanes with respect to activity, selectivity toolefins (particularly monoolefins), and rate of deactivation.

The above objects are realized by the various aspects of the inventiondescribed below.

According to one aspect, in a process for preparing a dehydrogenationcatalyst of the type in which a support comprising zinc aluminate isimpregnated with at least one of platinum and tin from an impregnationsolution, the improvement comprises simultaneously impregnating thesupport with the platinum and the tin by contacting the support with animpregnation solution which comprises, in solution, a tin compound, aplatinum compound, and a carboxylic acid.

According to other aspects of the invention, there is provided adehydrogenation catalyst produced according to the above-describedprocess, and also a process of using such catalyst in thedehydrogenation of at least one alkane containing 2-8 carbon atoms permolecule, in the presence of steam, to at least one alkene.

It is shown in a subsequent example that a dehydrogenation catalystprepared in accordance with the invention demonstrates, in thedehydrogenation of an alkane, higher activity, higher selectivity toolefins (particularly monoolefins), and a slower rate of deactivationthan comparative catalysts produced in accordance with prior artprocesses.

DETAILED DESCRIPTION OF THE INVENTION

In the presently preferred method of preparing the zincaluminate-containing support, the zinc aluminate is prepared by a methodcomprising mixing (preferably dry-mixing in a suitable mill) appropriateamounts (preferably approximately equimolar amounts) of zinc oxide andalumina, adding water or a dilute aqueous acid solution such as a diluteacetic acid solution while mixing is continued, drying the resulting wetmixture (preferably at about 150°-250° C.), and then calcining(preferably by heating in air) the dried mixture at a sufficiently hightemperature (preferably at about 750°-1200° C., more preferably about750°-1000° C.) for a sufficient length of time (preferably about 1-10hours) to form zinc aluminate. The alumina employed can be in anysuitable form, such as hydrated or flame-hydrolyzed, but is preferablyhydrated alumina and most preferably an a lumina monohydrate such asboehmite or pseudoboehmite. Various other additives, such as graphiteand/or calcium aluminate, can also be present during the mixing step.The inclusion of calcium aluminate in the support is particularlypreferred. The time required for thorough dry-mixing and subsequentmixing with the water or aqueous acid solution depends on the particularmixing equipment, amounts of ingredients to be mixed, and otheroperating parameters. The above-described dried mixture can beappropriately moistened with water and then extruded, tabletted,granulated, or processed to any other suitable form prior to calcining.A suitable lubricant such as zinc stearate can be employed, if desired,in such processing of the dried mixture.

After preparation of the support, such support is simultaneouslyimpregnated with platinum and tin by contacting the support with animpregnation solution comprising at least a platinum compound, a tincompound, and a carboxylic acid. This contacting step can be carried outin any suitable manner, such as by spraying the support with theimpregnation solution or by immersing the support in the impregnationsolution a sufficient time so that substantially all of the platinum andtin in solution diffuses into the support. When spraying the support, itis typical to employ a volume of impregnation solution which isapproximately equivalent to the pore volume of the support, preferablyfollowed by a suitable "aging" period of about 0.1-24 hours, morepreferably about 0.25-1 hour, to allow substantially all of the platinumand tin in solution to diffuse into the support. Where the support isimmersed in impregnation solution, it is typical to employ a volume ofsolution which is about 1-2 times the volume of support beingimpregnated.

As to the composition of the impregnation solution, such solutioncomprises, as mentioned above, a platinum compound, a tin compound, anda carboxylic acid in solution, and preferably further comprises aninorganic acid. Most preferably, the impregnation solution is an aqueoussolution consisting essentially of water, the platinum compound, the tincompound, the carboxylic acid, and the inorganic acid. The preferredweight percentages of the platinum of the platinum compound, the tin ofthe tin compound, the carboxylic acid, and the inorganic acid are asfollows, respectively, based on the weight of the support: preferablyabout 0.05-5 weight percent, and most preferably 0.1-1 weight percent ofthe platinum; preferably about 0.1-5 weight percent, and most preferably0.5-2 weight percent of the tin; preferably about 1-30 weight percent,most preferably 5-20 weight percent of the carboxylic acid; andpreferably about 0.1-10 weight percent, and most preferably 1-5 weightpercent of the inorganic acid. The concentrations of the platinumcompound, tin compound, the carboxylic acid, and the inorganic acid aspresent in a suitable solvent, such as water, are not particularlycritical as long as such components remain in solution and are presentin the desired amounts relative to the weight of the support.

Any platinum compound capable of impregnating the support with platinumfrom the impregnation solution can be employed in accordance with theinvention. Suitable platinum compounds include platinum chloride,chloroplatinic acid, ammonium chloroplatinate, platinum diammineoxalate, and platinum tetrammine chloride. Chloroplatinic acid isparticularly preferred.

Any tin compound capable of impregnating the support with tin from theimpregnation solution can be employed in accordance with the invention.Suitable tin compounds include tin halides, nitrates, oxalates,acetates, oxides, and hydroxides. Tin halides are preferred, andstannous chloride is particularly preferred.

The carboxylic acid is defined herein and in the appended claims as anyorganic acid having at least one terminal carboxyl (COOH) group.Preferred carboxylic acids include oxalic acid, formic acid, aceticacid, citric acid, and succinic acid. Oxalic acid is particularlypreferred.

Suitable inorganic acids include, for example, hydrochloric acid, nitricacid, sulfuric acid, hydrofluoric acid, and phosphoric acid.Hydrochloric acid is most preferred.

The various components of the impregnation solution can be mixedtogether in any sequence in accordance with certain broad aspects of theinvention, but it is most preferred to form the impregnation solutionfrom the combination of (i) a first solution comprising the platinumcompound and the carboxylic acid and (ii) a second solution comprisingthe tin compound and the inorganic acid. Each of the first and secondsolutions are preferably aqueous solutions . It is also preferred toheat the resulting impregnation solution to a temperature of about 20°C.-90° C., most preferably about 40° C.-60° C., immediately prior toimpregnation of the support in order to facilitate dissolving of thevarious components and also to facilitate diffusion of the platinum andtin into the support.

Following impregnation, the impregnated support is preferably dried at atemperature of about 80°-250° C., followed by calcining in anoxygen-containing atmosphere (i.e. air) at a temperature of about400°-600° C. The resulting calcined catalyst is then preferably washedwith water to remove any ions (i.e. chloride), and is subsequently driedagain.

The catalyst produced as described above generally contains thefollowing components in the specified weight percentages as based on theweight of the catalyst: about 80-98 weight percent zinc aluminate; about0.05-5 weight percent platinum; about 0.1-5 weight percent tin; andaccording to a preferred embodiment, about 1-20 weight percent calciumaluminate. It is understood that additional components which arebeneficial for catalyzing the dehydrogenation of alkanes may also bepresent in small amounts, such as Re, Au, Ag, alkali metal, Ce, and thelike. Generally, the surface area of the catalyst is in the range offrom about 5 to about 100 m² /g. The catalyst particles can have anysuitable size and shape, such as cylindrical, spherical, granules, ortrilobal.

Any suitable alkane containing 2-8 carbon atoms per molecule can be usedas feed in the dehydrogenation process of this invention such as, forexample, ethane, propane, n-butane, isobutane, n-pentane, isopentane,and mixtures thereof. Particularly preferred is isopentane.

The operating conditions of alkane dehydrogenation are well known. Steamis present to alleviate coke deposition on the catalyst, to enhance feedconversion, and to retard catalyst deactivation. The reactiontemperature is considerably higher than the normal boiling temperature(measured at 1 atm.) of the feed alkane, and is generally in the rangeof about 500° C.-650° C., preferably about 560°-610° C. The molar ratioof steam to the alkane(s) in the vaporized feed is generally in therange of from about 0.5:1 to about 30:1, preferably from about 2:1 toabout 10:1. The pressure is generally in the range of from about 0 toabout 200 psig, and preferably about 20 to about 100 psig.

In the dehydrogenation process, steam and vaporized alkane, preferablypremixed at the desired molar ratio, ere generally preheated and passedthrough the dehydrogenation reactor (or a train of two or more reactorsin series or in parallel) containing a fixed bed of the catalyst. Thegas hourly space velocity of the vaporized alkane feed (excluding steam)in the dehydrogenation process is generally in the range of from about100 to about 10,000 cc alkane per cc catalyst per hour, preferably fromabout 500 to about 2,000 cc/cc/hour. The flow rate of steam isdetermined by the desired molar ratio of steam to alkane feed. Freeoxygen is substantially absent during the dehydrogenation since O₂causes the formation of higher amounts of undesirable carbon oxides (COand/or CO₂) during the process.

During the dehydrogenation process, the catalyst loses some of itscatalytic activity, in part because of coke formation on the catalystsurface. When the catalytic activity has dropped below an effectivelevel (generally after about 6-30 hours on stream), the flow of thealkane-containing feed is cut off, and a purge of gas comprising steamand/or an inert gas (e.g., N₂, Ar, He) is passed through the hotcatalyst bed (at a temperature of about 500°-650° C., for about 1-60minutes), so as to substantially remove hydrocarbons from the reactor.Subsequently, the catalyst is regenerated, preferably by treating thecatalyst for a suitable time with a free oxygen-containing gas,preferably a stream of steam-diluted air. Generally, the regenerationtemperature is in the range of from about 450° to about 750° C., and themolar ratio of steam to free oxygen is in the range of from about 20:1to about 200:1. The pressure during regeneration is generally about0-200 psig, preferably about 20-100 psig. The duration of regenerationdepends on the regeneration conditions and on the amount of cokedeposits to be removed. Generally, regeneration is carried out for about0.1 to about 5 hours, preferably about 0.2 to about 1 hour. Thereafter,the reactor is purged again with a gas comprising steam and/or an inertgas (to sweep out O₂), the flow of the alkane feed is resumed, and thedehydrogenation is carried out with the regenerated catalyst compositionuntil catalyst regeneration is again required.

The product mixture of the dehydrogenation process comprises primarilymonoolefins (alkenes). By-products include CO, C₂, paraffins, anddiolefins. When isopentane is used as feed, primarily C₅ monoolefins,such as 3-methylbutene-1, 2-methylbutene-1, 2-methylbutene-2, areformed. The thus formed monoolefinic hydrocarbons can be recovered afterhaving been separated from other components of the product mixture ofthe dehydrogenation process by any suitable means, e.g., by fractionaldistillation, absorption/desorption processes, or membrane separationtechniques. Unreacted feed, after it has been substantially separatedfrom other product mixture components, can be recycled to thedehydrogenation reactor which contains the catalyst.

It is understood that reasonable modifications and variations of theinvention can be made without departing from the scope of thisinvention.

An example will now be described to further illustrate the invention,but which should not be construed to limit the invention in any manner.

EXAMPLE

The purpose of this example is to compare dehydrogenation resultsobtained with three separate catalysts (Catalysts A, B, and C) whichwere prepared employing different preparation processes. Catalysts A andB are comparative catalysts and Catalyst C is an invention catalyst.Preparation of such catalysts are described below.

Catalyst A (Comparative--incorporation of tin into support material andsubsequent impregnation of support with platinum from aqueous solutioncontaining platinum compound): 939 g of a boehmite alumina (VistaChemical Company, Houston, Tex., under the product designation"Dispal"), 597 g of zinc oxide (Zinc Corporation of America, Monaca,Pa.), 19.5 g of stannic oxide (Harshaw Chemical Co., Cleveland, Ohio),and 150 g of calcium aluminate (Secar 71 Cement, from LaFarge CalciumAluminates , Chesapeake, Va.) were dry mixed in a mix muller for 10minutes. To the dry mixture was added 825 mL, of an aqueous 1 volumepercent acetic acid solution over a period of 3 minutes while mixing wascontinued. The resulting paste was dried at 200° C. overnight in a BlueM circulating air oven. The dried material was ground, sieved through a30 mesh screen, and the fraction which passed through the screen wassprayed with sufficient water to bring the moisture level to about 10-11weight percent, as based on the total weight of the thus moistenedmaterial. 34 g of zinc stearate was blended with the resulting material,followed by tabletting in a tabletting machine, equipped with dies tomake 1/8"×1/8" tablets, at a pressure of about 140 lb.

Thereafter, the tablets were calcined in air for 5 hours at 843° C.after having ramped to 843° C. over about 6 hours. An aqueousimpregnation solution of chloroplatinic acid, having a platinum contentsufficient to deposit about 0.6 weight percent (as based on total weightof catalyst) of platinum on the support, was sprayed onto the calcinedtablets. Coating of the calcined tablets with impregnation solution wasfacilitated by spraying such tablets while in a mixer that is rotatedabout its longitudinal axis at an acute angle with respect to vertical.The thus impregnated tablets were dried in air at 150° C. for 3 hoursand then calcined in flowing air at 525° C. for 3 hours after havingramped to the 525° C. temperature at a rate of 2° C./minute. In order tosubstantially remove chloride ions from the resulting calcined catalyst,the catalyst was washed for 3 hours in water at a temperature of 82°-99°C., followed by drying in air at 150° C. for 3 hours to result in thefinal catalyst. Such catalyst contained about 0.6 weight percentplatinum and about 1 weight percent tin, as based on the total weight ofthe catalyst.

Catalyst B (Comparative--simultaneous impregnation of support withplatinum and tin from an aqueous solution containing a platinumcompound, a tin compound, and an inorganic acid): In preparation of afirst batch of support tablets, 597 g of zinc oxide (described above),939 g of boehmite alumina (described above), and 150 g of less than 30mesh calcium aluminate (described above) were dry mixed in a mix-mullerfor 10 minutes. To the dry mixture was slowly added 825 mL of an aqueous1 volume percent acetic acid solution over a period of 15 minutes whilemixing was continued. Thereafter, 30 g of high purity graphite (KS-44graphite from Lonza Inc., Fairlawn, N.J.) was added, with mixing, over aperiod of 15 minutes. The resulting paste was dried at 200° C. overnightin a Blue M circulating air oven. The dried material was ground, sievedthrough a 30 mesh sieve, and the resulting fraction of less than 30 meshwas sprayed with sufficient water to bring the moisture content up to10.51 weight percent, as based on the total weight of the thus moistenedmaterial. The resulting moist material was tabletted in the mannerdescribed for Catalyst A, and then calcined in air in a muffle furnaceat 843° C. for 5 hours after having ramped to 843° C. over about 6hours.

A second batch of support tablets was prepared in the same manner as thefirst batch, except that the material resulting from grinding andsieving was sprayed with sufficient water to bring the moisture contentup to 10.01 weight percent instead of 10.51 weight percent. Such secondbatch was mixed with the first batch of support tablets to result in ablended batch of support tablets. 210 g of such blended batch of supporttablets were then dried in air at 150° C. for 2 hours. 100 g of suchdried support tablets were employed to produce Catalyst B as describedbelow.

A first solution was prepared by dissolving 1.58 g of chloroplatinicacid crystals in 25 mL of water. A second solution was prepared bydissolving 1.92 g of hydrated stannous chloride (SnCl₂.2H₂ O) in 3.0 mLof concentrated hydrochloric acid (aqueous solution containing about 37weight percent HCl) . The thus prepared first and second solutions weremixed and heated to 50° C. to result in the desired impregnationsolution. The above-mentioned 100 g of support tablets were sprayed withthe impregnation solution in the same general manner as described forCatalyst A to result in impregnated tablets which were allowed to age atroom temperature for about 30 minutes. The impregnated tablets were thendried in air overnight at 150° C., followed by calcining in flowing airin accordance with the following schedule: ramp from ambient temperatureto 149° C. at 2° C./minute and hold at 149° C. for 1 hour; ramp from149° C. to 266° C. at 2° C./minute and hold at 266° C. for 2 hours; rampfrom 266° C. to 524° C. at 2° C./minute and hold at 524° C. for 5 hours;and allowing cooling to room temperature over about 3-4 hours. Chlorideions were substantially removed from the resulting calcined catalyst bywashing with 15 gallons of water over a 6 hour period, followed bydrying overnight in air at 150° C. to result in the final catalyst. Suchcatalyst contained about 0.6 weight percent platinum and about 1 weightpercent tin, as based on the total weight of the catalyst.

Catalyst C (Invention--simultaneous impregnation of support withplatinum and tin from aqueous solution containing a platinum compound, atin compound, a carboxylic acid, and an inorganic acid): 100 g ofsupport tablets, from the blended batch described above, were employedto prepare this catalyst in the same manner as described for Catalyst B,except that the first solution was prepared by dissolving 15 g of oxalicacid in 25 mL of water, adding 1.58 g of chloroplatinic acid crystals,and then heating to 80° C. to facilitate dissolving of oxalic acid inthe water. Such first solution was mixed with the second solution toresult in the impregnation solution in the same manner as described forCatalyst B, followed by the remaining steps of catalyst preparationwhich were also identical to those described for Catalyst B. The finalCatalyst C contained about 0.6 weight percent platinum and about 1weight percent tin, as based on the total weight of the catalyst.

Dehydrogenation Runs--Each of Catalysts A, B, and C were employed in thedehydrogenation of isopentane in a laboratory reactor having a length ofabout 1 foot and a diameter of about 1 inch. With respect to eachcatalyst, the reactor was loaded with multiple layers of materialincluding a catalyst layer (6.0 g) about 1-11/2 inches high, an upperlayer of alumina about 5-6 inches high above the catalyst layer, and alower layer of alumina about 1 inch high below the catalyst layer.

Liquid isopentane was vaporized and introduced into the reactor at aflow rate of 24 cc/hour, and superheated steam was introduced into thereactor at a flow rate of 25.2 cc/hour to provide an isopentane/steammixture having a steam to isopentane molar ratio of 6:1. Other processconditions included a catalyst bed temperature of 580° C. and a reactorpressure of 50 psia. The exiting product gas was analyzed by means of agas chromatograph.

Dehydrogenation runs for each catalyst were carried out in a cyclic,continuous flow process with intermediate air regeneration, where eachcycle consisted of the following steps at the above-describedtemperature and pressure: a regeneration step consisting of flushing ofthe catalyst with nitrogen for 15 minutes at a flow rate of about 125cc/minute, passing air for at least 60 minutes at a flow rate of 125cc/minute over the catalyst, and then another 15 minute nitrogen purgeof the catalyst; and then a conversion or dehydrogenation step ofpassing the isopentane/steam mixture through the reactor and catalystfor about 7 hours. Three such cycles were carried out with eachcatalyst.

Conversion and selectivity results for Catalyst A, B, and C are setforth in Table I. Converted products for each catalyst includedprimarily C₅ monoolefins such as 3-methylbutene-1, 2-methylbutene-1, and2-methylbutene-2, but also included small amounts of by-products such ascarbon monoxide, carbon dioxide, paraffins, and diolefins. Conversion inTable I is given in terms of mole percent of the feed (isopentane), andselectivities are given in terms of mole percent of the converted feed.Data is provided in Table I for each of the three cycles for productcollected at 1.25 hour and 4.25 hours into the conversion(dehydrogenation) step of each respective cycle. An average of data at1.25 and 4.25 hours is also provided.

                  TABLE I                                                         ______________________________________                                        Dehydrogenation of Isopentane Using Catalysts A, B, and C                                                 Selectivity to                                    Conversion     Selectivity to                                                                             Monoolefins                                       (mole %)       Olefins (mole %)                                                                           (mole %)                                          A        B      C      A    B    C    A    B    C                             ______________________________________                                        Cycle                                                                         1.25 hr.                                                                            NM.sup.a                                                                             31.9   55.1 NM   80.6 91.9 NM   70.5 84.0                        4.25 hr.                                                                            NM     25.2   49.1 NM   82.1 90.7 NM   68.6 79.9                        Aver- NM     28.8   51.7 NM   81.0 91.4 NM   68.8 82.3                        age                                                                           Cycle                                                                         2                                                                             1.25 hr.                                                                            53.0   41.0   56.8 88.2 83.1 91.5 80.6 73.9 83.5                        4.25 hr.                                                                            41.3   31.0   47.3 88.7 85.6 91.6 79.2 72.9 82.7                        Aver- 46.7   35.8   52.5 88.5 84.3 91.3 80.1 73.2 82.7                        age                                                                           Cycle                                                                         3                                                                             1.25 hr.                                                                            56.7   34.6   60.2 88.7 84.6 93.0 81.1 74.1 85.1                        4.25 hr.                                                                            45.0   26.6   50.0 89.4 85.1 91.7 80.7 70.0 82.5                        Aver- 50.8   30.7   55.0 89.1 84.1 91.8 81.0 71.5 83.2                        age                                                                           ______________________________________                                         .sup.a NM means no measured.                                             

It can be seen from Table I that Catalyst C, in accordance with theinvention, provided consistently higher conversion, higher selectivityto olefins, and higher selectivity to monoolefins than comparativeCatalysts A and B in the dehydrogenation of isopentane.

Set forth in Table II Is the decrease (%) in conversion from theconversion percentage at 1.25 hr. to the conversion percentage at 4.25hr. for each of the catalysts and their respective cycles. Calculationof this decrease in conversion provides a good indication of the rate ofdeactivation of the catalyst during the dehydrogenation step of aparticular cycle.

                  TABLE II                                                        ______________________________________                                        Decrease in Conversion for Catalysts A, B, and C                              in Cycles 1, 2, and 3                                                                 Conversion Decrease (%)                                               Cycle     A              B     C                                              ______________________________________                                        1         ND.sup.a       21    11                                             2         22             24    17                                             3         21             23    17                                             ______________________________________                                         .sup.a ND means not determined due to lack of data.                      

It can be seen from Table II that conversion decreased to a lesserextent in each cycle for Catalyst C as compared to Catalysts A and B,indicating a desirably slower rate of deactivation for Catalyst C.

That which is claimed is:
 1. In a process for preparing adehydrogenation catalyst comprising the step of impregnating a supportcomprising zinc aluminate with platinum and tin from an impregnationsolution, the improvement which comprises contacting the support with animpregnation solution which has been formed by combining a firstsolution consisting essentially of water, a platinum compound and oxalicacid and a second solution consisting essentially of water, a tincompound and an inorganic acid.
 2. A process as recited in claim 1wherein the inorganic acid is hydrochloric acid.
 3. A process as recitedin claim 1 wherein the platinum compound is chloroplatinic acid and thetin compound is stannous chloride.
 4. A process as recited in claim 1wherein platinum of the platinum compound, tin of the tin compound,oxalic acid, and the inorganic acid are present in said impregnatingsolution in the following weight percentages as based on the weight ofthe support: about 0.05-5 weight percent of platinum; about 0.1-5 weightpercent of tin; about 1-30 weight percent of oxalic acid; and about0.1-10 weight percent of the inorganic acid.
 5. A process as recited inclaim 4 wherein the support further comprises calcium aluminate.
 6. Adehydrogenation catalyst produced in accordance with claim
 1. 7. Adehydrogenation catalyst produced in accordance with claim
 4. 8. Adehydrogenation catalyst produced in accordance with claim
 5. 9. Aprocess in accordance with claim 1 comprising the additional steps ofdrying the support which has been contacted with said impregnatingsolution, and calcining the thus-obtained dried, impregnated support inan oxygen-containing atmosphere at a temperature of about 400°-600° C.10. A process in accordance with claim 9 wherein said drying is carriedout at a temperature of about 80°-250° C.
 11. A process in accordancewith claim 9 further comprising the steps of washing the calcined,impregnated support obtained by the process of claim 9 with water so asto remove chloride ions therefrom, and then drying the thus-obtainedwashed catalyst material.
 12. A process in accordance with claim 5,wherein said dehydrogenation catalyst contains about 80-98 weightpercent zinc aluminate, about 0.05-5 weight percent platinum, about0.1-5 weight percent tin, and about 1-20 weight percent calciumaluminate.
 13. A dehydrogenation catalyst produced in accordance withclaim 12.